The present invention relates to the filtering of particulates from fluids, particularly the removal of solids from water, using compressible filter media in a compressible housing.
Prior art techniques using compressible media have relied on mechanically actuated plates to externally compress filter media.
For example, U.S. Pat. No. 5,248,415 to Masuda et al. discloses the use of fibrous filter media compressed by a movable bottom plate in a bottom-up filtration apparatus.
U.S. patent application Publication No. US2003/0111431 discloses fibrous filter media compressed by a movable top plate in a bottom-up filtration apparatus. U.S. Pat. No. 4,776,962 discloses a fibrous filter media compressed by a movable top plate in a downflow filtration apparatus.
In such prior art apparatuses, the movable plate compresses the filter media within rigid containment walls during filtration and provides compression across the entire filter media bed. Compression of the media increases the filtering performance measured as percent removal and removal of smaller particulates; however, particulate rapidly builds up in the initial portion of the media bed and reduces the filter operation time. Filtering efficiency progressively decreases as a result of the particulate accumulation, and eventually filtering must be stopped to wash and dislodge the solid build up. The movable plate pressed against the media further inhibits the capacity of the initial portion of the media bed to remove particulates resulting in shorter filter operation time and less solid removal per unit of filter media. The washing operation requires that the movable plate be retracted so that air and washing fluid may be directed through the media to scrub and dislodge the solids. The media is re-compressed with the movable plate when filtering is restarted. The movable plates require close tolerance with the rigid containment walls to retain filter media and maintain efficient filter and backwashing operations.
Accordingly, there is a need for a filter apparatus and method that provides efficient filtration with compressed media that improves particulate capture with longer filter operation times, but eliminates the need for mechanically movable plates, close tolerance containment walls and associated mechanisms.